Super-junction structure and method for manufacturing the same and semiconductor device thereof

ABSTRACT

The present disclosure relates to a super-junction structure, a method for manufacturing the super-junction structure and a semiconductor device including the super-junction structure. The super-junction structure includes an epitaxy layer of a first doping type and a plurality of first pillar regions of a second doping type which are formed in the epitaxy layer and are separated from each other. Each of the first pillar regions has a doping concentration that decreases from bottom to top. A portion of the epitaxy layer between adjacent ones of the first pillar regions is a second pillar region. The first pillar regions and the second pillar region are arranged alternatively to form the super-junction structure. The first pillar regions are characterized by the doping concentration that decreases from bottom to top so that the super-junction structure has a relatively high breakdown voltage and a relatively low on resistance. Moreover, the super-junction structure changes a path of an avalanche current and thus suppresses an avalanche current so that the device is not easily damaged.

CLAIM OF PRIORITY

This application claims priority to Chinese Application No.201410441028.9, filed Sep. 1, 2014 (published as CN 10421376 A), whichis hereby incorporated by reference.

BACKGROUND OF THE DISCLOSURE

1. Field of the Disclosure

The present disclosure relates to semiconductor devices, and moreparticularly, to a super-junction structure, a method for manufacturingthe super-junction structure and a semiconductor device including thesuper-junction structure.

2. Description of the Related Art

High-power semiconductor devices, such as metal-oxide-semiconductorfield effect transistors (MOSFETs), insulated gate bipolar transistors(IGBTs) and the like, typically decreases a doping concentration of adrift region for a high breakdown voltage. However, the drift regionwill have a large on resistance if having a low doping concentration.Thus, the conventional approach cannot take into account both a highbreakdown voltage and a low on resistance.

To achieve both a high breakdown voltage and a low resistance insemiconductor devices, a super-junction structure may be used as a driftregion, instead of a simple epitaxy layer. The super-junction structureis a structure in which N-type pillar regions and P-type pillar regionsare arranged alternatively. FIG. 1 is a structural diagram of asuper-junction structure as a drift region of a MOSFET according to theprior art. As shown in FIG. 1, a plurality of P-type pillar regions areformed in an N-type epitaxy layer and are separated from each other. AnN-type pillar region is located between two adjacent P-type pillarregions. The P-type region and the N-type pillar regions are arrangedalternatively in the epitaxy layer to form a super-junction structure.The super-junction structure achieves both a high breakdown voltage anda low on resistance in the MOSFET.

When a voltage is applied to a substrate of the MOSFET, an avalanchecurrent occurs and flows from a source region to a drain region. TheP-type pillar regions are doped uniformly, and the P-type well regionsare located at the top surfaces of the P-type pillar regions and have adoping concentration larger than that of the P-type pillar regions.Thus, the avalanche current flows into the P-type well regions at oneside and passes through a base resistor RB of a parasitic transistor BJTof the MOSFET. A large voltage drop occurs across the base resistor RBand turns on the parasitic transistor, which in turn amplifies theavalanche current and damage the device. Consequently, the conventionalsuper-junction structure cannot really suppress an avalanche currenteven in a case that the super-junction structure is used as a driftregion of the semiconductor device.

BRIEF DESCRIPTION OF THE DISCLOSURE

In view of this, the present disclosure provides a super-junctionstructure, a method for manufacturing the same, and a semiconductordevice including the same to solve the problem of suppressing anavalanche current over the conventional super-junction.

In a first embodiment, there is provided a super-junction structurecomprising an epitaxy layer of a first doping type, and a plurality offirst pillar regions of a second doping type, which are formed in theepitaxy layer and separated from each other, and a second pillar region,which is a portion of the epitaxy layer between adjacent ones of theplurality of first pillar regions and arranged alternatively with theplurality of first pillar regions to form the super-junction structure,

each of the plurality of first pillar regions comprises a firstsub-pillar region with a doping concentration larger that an averagedoping concentration of the plurality of first pillar regions, and asecond sub-pillar region with a doping concentration less than anaverage doping concentration of the plurality of first pillar regions;

wherein the average doping concentration is a doping concentration ofthe plurality of first pillar regions in a case that the plurality offirst pillar regions have a uniform doping concentration and theplurality of first pillar region has a dopant amount equal to that ofthe second pillar region.

Preferably, the first doping type is an N type and the second dopingtype is a P type.

In a second embodiment, there is provided a semiconductor device,comprising a semiconductor substrate, a super-junction structure asmentioned above, well regions of the second doping type, source regionsof the first doping type, a gate oxide, a polysilicon gate, a front-sidemetal layer and a back-side metal layer;

the super-junction structure is disposed above the semiconductorsubstrate;

the well region contacts top surfaces of the plurality of pillar regionsand a portion of the top surface of second pillar region;

the source region is arranged at a surface of the well region.

the gate oxide is arranged above the second pillar region, a portion ofthe well region and a portion of the source region;

the polysilicon gate is arranged above the gate oxide;

the front-side metal layer contacts the source region, and the back-sidemetal layer is arranged below and contacts the semiconductor substrate.

Preferably, the semiconductor device further comprises an extensionportion of the second pillar region, wherein the extension portion islocated above the second pillar region, below the gate oxide, andbetween adjacent ones of the well regions.

Preferably, the semiconductor device further comprises contact regionsat the surfaces of the well regions, wherein the front-side metal layercontacts the source regions and the contact regions.

In a third embodiment, there is provided a semiconductor device,comprising a first semiconductor layer, a super-junction structure asmentioned above, and a second semiconductor layer above thesuper-junction structure, wherein in a case that the first semiconductorlayer is of the first doping type, the second semiconductor layer is ofthe second doping type, and in a case that the first semiconductor layeris of the second doping type, the second semiconductor layer is of thefirst doping type.

In a fourth embodiment, there is provided a method for manufacturing thesuper-junction structure as mentioned above, comprising:

forming an epitaxial layer of a first doping type;

forming a plurality of first sub-pillar regions of a second doping typein the epitaxial layer, wherein the plurality of first sub-pillarregions are separated from each other and have a first dopingconcentration;

forming a plurality of second sub-pillar regions on the plurality offirst sub-pillar regions in the epitaxial layer, wherein the pluralityof second sub-pillar regions have a second doping concentration;

each of the plurality of first sub-pillar regions is aligned in avertical direction to and connected to respective one of the pluralityof second sub-pillar regions to form respective one of a plurality offirst pillar regions;

a portion of the epitaxy layer between adjacent ones of the plurality offirst pillar regions forms a second pillar region, the first dopingconcentration is larger than an average doping concentration of thefirst pillar regions, and the second doping concentration is less thatthe average doping concentration;

wherein the average doping concentration is a doping concentration ofthe plurality of first pillar regions in a case that the plurality offirst pillar regions have a uniform doping concentration and theplurality of first pillar region has a dopant amount equal to that ofthe second pillar region.

Preferably, the epitaxial layer comprises a plurality of sub-epitaxiallayers of the first doping type, and the first sub-pillar regions andthe second sub-pillar regions are formed in the epitaxial layer in thefollowing steps:

a) forming one of the plurality of sub-epitaxial layers;

b) doping the sub-epitaxial layer with a dopant of a second type to forma plurality of pillar regions which are separated from each other andhave the first doping concentration;

c) forming a second sub-epitaxial layer on a surface of the abovestructure;

d) repeating step b);

e) repeating steps c) and d) for a predetermined times;

f) repeating step c);

g) doping the second sub-epitaxial layer with a dopant of a second typeto form a plurality of pillar regions which are separated from eachother and have the second doping concentration less than the firstdoping concentration;

h) repeating steps f) and g) for a predetermined times,

wherein each of the plurality of pillar regions formed in a previousstep is aligned in a vertical direction to and connected to respectiveone of the plurality of pillar regions formed in a subsequent step, toform the plurality of first sub-pillar regions by connecting the pillarregions having the first doping concentration, and to form the pluralityof second sub-pillar regions by connecting the pillar regions having thesecond doping concentration.

Preferably, after forming the epitaxial layer and before forming thefirst sub-pillar regions, the method further comprises forming aplurality of trenches in the epitaxial layer;

the second pillar region is located between adjacent ones of theplurality of trenches;

forming the plurality of first sub-pillar regions at lower portions ofthe plurality of trenches by filling the lower portion with a firstdoped layer of the first doping type;

forming the plurality of second sub-pillar regions on the plurality offirst sub-pillar regions by filling upper portions of the plurality oftrenches with a second doped layer of the second doping type and havingthe second doping concentration.

Preferably, after forming the epitaxial layer and before forming thefirst sub-pillar regions, the method further comprises forming aplurality of trenches in the epitaxial layer;

forming the plurality of first sub-pillar regions at bottoms of theplurality of trenches by doping the bottoms of the plurality oftrenches, forming the plurality of second sub-pillar regions on theplurality of first sub-pillar regions by filling the plurality oftrenches with a second doped layer of the second doping type and havingthe second doping concentration.

To sum up, the super-junction structure according to the presentdisclosure includes first pillar regions having first sub-pillar regionswith a large doping concentration and second sub-pillar regions with alow doping concentration from bottom to top. When a high voltage isapplied to the semiconductor device including the super-junctionstructure, an avalanche current flows into the first pillar regions fromthe first sub-pillar regions with the high doping concentration.Consequently, a path of the current is changed. The first pillar regionsare characterized by the doping concentration that decreases from bottomto top so that the super-junction structure has a relatively highbreakdown voltage and a relatively low on resistance. Moreover, thesuper-junction structure changes a path of an avalanche current and thussuppresses an avalanche current so that the device is not easilydamaged.

BRIEF DESCRIPTION OF THE DRAWINGS

Those technical solutions according to embodiments of the presentdisclosure and the prior art will be apparent when they are described inconnection with appended drawings which are firstly described brieflyhereinbelow. It will be obvious to one skilled in the art that thefollowing appended drawings show only some embodiments of the presentdisclosure. Other appended drawings can be obtained from these appendeddrawings without the need for creative work.

FIG. 1 is a structural diagram of a super-junction structure of a MOSFETaccording to the prior art;

FIG. 2 is a structural diagram of a super-junction structure accordingto an embodiment of the present disclosure;

FIG. 3 is a structural diagram of a semiconductor device according to anembodiment of the present disclosure;

FIG. 4 is a structural diagram of a semiconductor device according toanother embodiment of the present disclosure;

FIGS. 5 a-5 c are cross-sectional views of semiconductor structures atvarious stages of a method for manufacturing a super-junction structureaccording to an embodiment of the present disclosure;

FIGS. 6 a-6 c are cross-sectional views of semiconductor structures atvarious stages of another method for manufacturing a super-junctionstructure according to an embodiment of the present disclosure; and

FIGS. 7 a-7 b are cross-sectional views of semiconductor structures atvarious stages of a further method for manufacturing a super-junctionstructure according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE DISCLOSURE Brief Descriptionof the Drawings Detailed Description of Embodiments of the Invention

Reference will now be made in detail to particular embodiments of thedisclosure in conjunction with appended drawings, so that objectives,features and advantages of the disclosure will become more apparent. Forthe purpose of clarity, some parts in the appended drawings are notdrawn to scale. Further, for simplicity, a structure may be shown in onedrawing while it may be actually obtained after several steps, and somewell-known details may be omitted.

Some particular details will be described for thorough understanding ofthe present disclosure. However, the present disclosure may be practicedwith or without these particular details by one skilled person, withoutdeparting the principles of the present disclosure. Thus, the presentdisclosure is not limited to the particular embodiments below.

FIG. 2 is a structural diagram of a super-junction structure accordingto an embodiment of the present disclosure.

Referring to FIG. 2, an embodiment of the present disclosure is relatedto a super-junction structure formed on a substrate 21. Thesuper-junction structure includes an epitaxy layer 22 of a first dopingtype, and a plurality of first pillar regions 23 of a second dopingtype, which are formed in the epitaxy layer 22 and separated from eachother, and a second pillar region 22′, which is a portion of the epitaxylayer 22 between adjacent ones of the plurality of first pillar regions23 and arranged alternatively with the plurality of first pillar regions23 to form the super-junction structure.

Each of the plurality of first pillar regions 23 comprises a firstsub-pillar region 23-1, i.e. a portion near the substrate 21, with adoping concentration larger than an average doping concentration of theplurality of first pillar regions 23, and a second sub-pillar region23-2, i.e. a portion far away from the substrate 21, with a dopingconcentration less than an average doping concentration of the pluralityof first pillar regions.

The average doping concentration is a doping concentration of theplurality of first pillar regions 23 in a case that the plurality offirst pillar regions 23 have a uniform doping concentration and have adopant amount equal to that of the second pillar region 22′.

In the super-junction structure according to an embodiment of thepresent disclosure, the first type is one of an N type and a P type, andthe second type is the other of the N type and the P type. The firstdoping type may be obtained by doping or diffusing a dopant of a firsttype into a semiconductor layer or region, and the second doping typemay be obtained by doping or diffusing a dopant of a second type into asemiconductor layer or region. The dopant of the first type is that ofone of an N type and a P type, and the dopant of the second type is thatof the other of an N type and a P type. The semiconductor materialincludes for example group III-V semiconductor, such as GaAs, InP, GaN,and SiC, and group IV semiconductor, such as Si, and Ge. The N-typedoping region may be of an N⁻-type or an N⁺-type, and the P-type dopingregion may be of a P⁻-type or a P⁺-type. The N-type or P-type indicatesto be lightly doped with a low doping concentration, and the N⁺ type orP⁺ type indicates to be heavily doped with a high doping concentration.In this and the following embodiments, the first doping type is an Ntype, and the second doping type is a P type, as an example only. Itwill be understood by one skilled person that the super-junctionstructure in these embodiments can also be implemented in a case thatthe first doping type is a P type, and the second doping type is an Ntype. A P-type doping region is formed by implanting or diffusing aP-type dopant in a semiconductor layer or region, for example, atrivalent acceptor impurity such as B, Al, and the like. An N-typedoping region is formed by implanting or diffusing an N-type dopant in asemiconductor layer or region, for example, a quinquevalent donorimpurity such as P, As, and the like.

In the super-junction structure according to the embodiment of thepresent disclosure, the first pillar regions 23 are P-type dopedsemiconductor regions, and the second pillar region 22′ is an N-typedoped semiconductor region. The first pillar regions 23 and the secondpillar region 22′ constitute a super-junction structure, i.e. super PNjunction structure. Different from a conventional super-junctionstructure, the first pillar regions 23 are P-type doped regions with anon-uniform doping concentration. Instead, the first pillar regions 23has a doping concentration that decreases from bottom to top, includinga first sub-pillar region 23-1 of a P-type with a relatively high dopingconcentration (i.e. P⁺) and a second sub-pillar region 23-3 of an N typewith a relatively low doping concentration (i.e. P⁻). The dopingconcentration of the first sub-pillar region 23-1 is larger than anaverage doping concentration of the first pillar regions 23, and thedoping concentration of the second sub-pillar region 23-2 is smallerthan an average doping concentration of the first pillar regions 23, sothat the first pillars have a dopant amount equal to or slightly largerthan that of the second pillar region 22′. In a case that thesuper-junction structure with the above structural features is used in ahigh-power device, such as MOSFET, IGBT and the like, an avalanchecurrent flows in a path excluding a parasitic resistor of well regions,when a high voltage is applied. Accordingly, the parasitic transistorwill not be turned on to amplify the avalanche current. Thesemiconductor device will have an improve performance for suppressingthe avalanche current.

Thus, the super-junction structure according to the embodiment of thepresent disclosure has a relatively high breakdown voltage and arelatively low on resistance, and suppresses an avalanche current sothat the semiconductor device is not damaged.

FIG. 3 is a structural diagram of a semiconductor device according to anembodiment of the present disclosure.

Referring to FIG. 3, an embodiment of the present disclosure is relatedto a semiconductor device. The semiconductor device includes asemiconductor substrate 31, a super-junction structure as mentionedabove, well regions 34 of the second doping type, source regions 35 ofthe first doping type, a gate oxide 37, a polysilicon gate 38, afront-side metal layer 39 and a back-side metal layer 310. Thesuper-junction structure includes an epitaxy layer 32 of a first dopingtype, and a plurality of first pillar regions 33 of a second dopingtype, which are formed in the epitaxy layer 32 and separated from eachother, and a second pillar region 32′, which is arranged betweenadjacent ones of the first pillar regions 33. The first pillar regions33 include a first sub-pillar region 33-1 and a second sub-pillar region33-2 from bottom to top.

The well regions 34 contact top surfaces of the first pillar regions 33and a portion of the top surface of second pillar region 32′. It shouldbe noted that in a case that the above super-junction structure is usedin the semiconductor device according to an embodiment of the presentdisclosure, the second pillar region 32′ has an extension portionextending upward. That is, the semiconductor device further comprises anextension portion 32″ above the second pillar region 32′, below the gateoxide 37, and between adjacent ones of the well regions 34. In a casethat the above super-junction structure is used in the semiconductordevice according to the present disclosure, it will be understood by oneskilled person that the second pillar region should be extended with anextension region 32″ and how to form it.

The source regions 35 are located above the well regions 34. The gateoxide 37 is located above the second pillar region 32′, portions of thewell regions 34 and portions of the source regions 35. The polysilicongate 38 is located above the gate oxide 37. The front-side metal layer39 contacts the source regions 35, as source electrodes. The back-sidemetal layer 310 is located below the semiconductor substrate 31 andcontacts the semiconductor substrate 31, as drain electrodes.

In the semiconductor device according to the embodiment of the presentdisclosure, it further comprises contact regions 36 of the second dopingtype, at surfaces of the well regions 34. The front-side metal layer 39contacts the source regions 35 and the contact regions 36, as souredelectrodes.

In the semiconductor device according to the embodiment of the presentdisclosure, the first pillar regions 33 and the second pillar region 32′constitute a super-junction structure, in which the first pillar regionshave a dopant amount approximately equal to or slightly larger than thatof the second pillar region, with a ratio in a range between 1:1 to1.2:1. Due to such a super-junction structure, the semiconductor devicewill have both a relatively high breakdown voltage and a relatively lowon resistance. Moreover, the first sub-pillar regions 33-1 as lowerportions of the first pillar regions 33 have a doping concentrationlarger than that of the second sub-pillar regions 33-2 as upper portionsof the first pillar regions 33, and larger than an average dopingconcentration of the first pillar regions 33. Due to such a structure, abreakdown point will be located at the first sub-pillar regions 33-1having a relatively high doping concentration when the semiconductordevice is applied with a high voltage. An avalanche current flows intothe first pillar regions at the first sub-pillar regions 33-1 as the lowportions of the first pillar region 33, from the drain regions, and thenflows into the well regions 34 from the first sub-pillar regions 33-1,and finally flows into the front-side metal layer 39. Thus, theavalanche current IA will not flow into the well regions 34 at one sideof the well regions 34. Instead, the avalanche current changes its path,and flows in a path excluding a base resistor RB of the well regions 34.Thus, there is no a voltage drop at the base resistor RB of a parasitictransistor BJT of the well regions 34 for turning on the parasitictransistor BJT and amplifying the avalanche current IA. Thesemiconductor device can suppress the avalanche current.

In the semiconductor device according to the embodiment of the presentdisclosure, the substrate 31 may be doped as a P type or an N type. TheN-type doping region may be of an N⁻-type or an N⁺-type, and the P-typedoping region may be of a P⁻-type or a P⁺-type. The N⁻-type or P⁻-typeindicates to be lightly doped with a low doping concentration, and theN⁺-type or P⁺-type indicates to be heavily doped with a high dopingconcentration.

Accordingly, the semiconductor device according to the embodiment of thepresent disclosure has both a relatively high breakdown voltage and arelatively low on resistance, and suppresses an avalanche current sothat the device is not easily damaged.

FIG. 4 is a structural diagram of a semiconductor device according toanother embodiment of the present disclosure.

Referring to FIG. 4, another embodiment of the present disclosure isrelated to another semiconductor device. The another semiconductordevice includes a first semiconductor layer 41, a super-junctionstructure as mentioned above, and a second semiconductor layer 44 of thesecond doping type on the surface of the super-junction structure. Thefirst semiconductor layer 41 may be of a first doping type and thesecond semiconductor layer 44 may be of a second doping type, or viceversa. The super-junction structure includes an epitaxy layer 42 of afirst doping type, and a plurality of first pillar regions 43 of asecond doping type, which are formed in the epitaxy layer 42 andseparated from each other, and a second pillar region 42′, which isarranged between adjacent ones of the first pillar regions 43. The firstpillar regions 43 include a first sub-pillar region 43-1 and a secondsub-pillar region 43-2 from bottom to top.

The dopant of the first type is that of one of an N type and a P type,and the dopant of the second type is that of the other of an N type anda P type. The N-type doping region may be of an N⁻-type or an N⁺-type,and the P-type doping region may be of a P⁻-type or a P⁺-type. TheN⁻-type or N⁺-type indicates to be lightly doped with a low dopingconcentration, and the N⁺-type or P⁺-type indicates to be heavily dopedwith a high doping concentration. For example, in the presentembodiment, the first semiconductor layer may be an N⁺-type siliconlayer, the epitaxial layer 42 may be an N-type silicon layer, the firstsub-pillar regions 43-1 may be a P⁺-type silicon layer, the secondsub-pillar region 43-2 may be a P⁻-type silicon layer, and the secondsemiconductor layer may be P⁺-type silicon layer.

In the semiconductor device according to the embodiment of the presentdisclosure, the first pillar regions 43 and the second pillar Regina 42′are formed in the epitaxial layer 42 to form a super-junction structure.Moreover, the first pillar regions 43 have a doping concentration thatdecreases from bottom to top, so that the semiconductor device improvesthe performance of suppressing an avalanche current even in a case thatthe semiconductor device has the same breakdown voltage. That is, thesemiconductor device has better voltage endurance and can be used in ahigh-power integrated circuit.

An embodiment of the present disclosure relates to a method formanufacturing the super-junction structure as shown in FIG. 2. Thesuper-junction may be formed on a substrate. The method formanufacturing the super-junction structure includes:

forming an epitaxial layer of a first doping type;

forming a plurality of first sub-pillar regions of a second doping typein the epitaxial layer, wherein the plurality of first sub-regions areseparated from each other;

the first sub-pillar regions have a first doping concentration;

forming a plurality of second sub-pillar regions on the plurality offirst sub-pillar regions in the epitaxial layer;

the second sub-pillar regions have a second doping concentration;

each of the plurality of first sub-pillar regions is aligned in avertical direction to and connected to respective one of the pluralityof second sub-pillar regions to form respective one of a plurality offirst pillar regions;

a portion of the epitaxy layer between adjacent ones of the plurality offirst pillar regions forms a second pillar region, the first dopingconcentration is larger than an average doping concentration of thefirst pillar regions, and the second doping concentration is less thatthe average doping concentration;

wherein the average doping concentration is a doping concentration ofthe plurality of first pillar regions in a case that the plurality offirst pillar regions have a uniform doping concentration and theplurality of first pillar region has a dopant amount equal to that ofthe second pillar region.

The substrate may be one of a P type and an N type. The dopant of thefirst type is that of one of an N type and a P type, and the dopant ofthe second type is that of the other of an N type and a P type. TheN-type doping region may be of an N-type or an N⁺-type, and the P-typedoping region may be of a P⁻-type or a P⁺-type. The N-type or P⁻-typeindicates to be lightly doped with a low doping concentration, and theN⁺-type or P⁺-type indicates to be heavily doped with a high dopingconcentration. For example, in the present embodiment, the substrate maybe an N⁺-type silicon layer, the epitaxial layer may be an N-typesilicon layer, the first sub-pillar regions may be a P⁺-type siliconlayer, the second sub-pillar region may be a P⁻-type silicon layer.

In a case that the N-type epitaxial layer of the super-junctionstructure includes a plurality of sub-epitaxial layers, the method formanufacturing the super-junction structure on the N⁺-type substrate mayinclude the following steps.

a) forming an N⁻-type sub-epitaxial layer, such as an N⁻-type siliconlayer, as shown in FIG. 5 a;

b) doping the sub-epitaxial layer with a P⁺-type dopant to form aplurality of P⁺-type pillar regions which have the first dopingconcentration and are separated from each other, as shown in FIG. 5 b;

c) forming a second N-type sub-epitaxial layer on a surface of the abovestructure;

d) repeating step b);

e) repeating steps c) and d) for a predetermined times;

f) repeating step c);

g) doping the second sub-epitaxial layer with a P⁻-type dopant to form aplurality of P⁻-type pillar regions which are separated from each otherand have the second doping concentration less than the first dopingconcentration; and

h) repeating steps f) and g) for a predetermined times, as shown in FIG.5 c.

In the above steps, each of the plurality of pillar regions formed in aprevious step is aligned in a vertical direction to and connected torespective one of the plurality of pillar regions formed in a subsequentstep, to form the plurality of first sub-pillar regions by connectingthe P⁺-type pillar regions having the first doping concentration, and toform the plurality of second sub-pillar regions by connecting theP⁻-type pillar regions having the second doping concentration.

The embodiments of the present disclosure also include two methods forforming trenches, besides the above methods for forming the P⁺-typefirst sub-pillar regions and the P⁻-type second sub-pillar regions.

A first method for forming the trenches is shown in FIGS. 6 a-6 c. Afterforming an N-type epitaxial layer, a plurality of trenches are formed inthe epitaxial layer, which are separated from each other. A portion ofthe epitaxial layer between adjacent ones of the trenches is a secondpillar region. Then, P⁺-type first sub-pillar regions and P⁻-type secondsub-pillar regions are formed in the trenches from bottom to top. Asshown in FIG. 6 b, the P⁺-type first sub-pillar regions are formed atlower portions of the trenches by filling the lower portions of thetrenches with a P⁺-type layer, such as P⁺-type silicon layer. Finally,as shown in FIG. 6 c, the P⁻-type second sub-pillar regions are formedat upper portions of the trenches by filling the upper portions of thetrenches with a P⁻-type layer above the P⁺-type first sub-pillarregions, such as P⁻-type silicon layer. That is, each of the pluralityof first pillar regions comprises a first sub-pillar region, i.e. aportion near the substrate, and a second sub-pillar region, i.e. aportion far away from the substrate, from bottom to top in one of thetrenches.

A second method for forming the trenches is shown in FIGS. 7 a and 7 b.After forming an N⁻-type epitaxial layer, a plurality of trenches areformed in the epitaxial layer, which are separated from each other. Thefirst sub-pillar regions at bottoms of the trenches by doping thebottoms of the trenches with a P⁺-type dopant. Then, as shown in FIG. 7b, the P⁻-type second sub-pillar regions are formed at upper portions ofthe trenches by filling the upper portions of the trenches with aP⁻-type layer above the P⁺-type first sub-pillar regions. Thus, thefirst sub-pillar regions and the second sub-pillar regions constitutethe first pillar regions.

It should be noted that in the present disclosure, a P-type dopant maybe a trivalent acceptor impurity such as B, Al, and the like, and anN-type dopant may be a quinquevalent donor impurity such as P, As, andthe like. It should also be understood that the relational terms such as“first”, “second”, and the like are used in the context merely fordistinguishing one element or operation from the other element oroperation, instead of meaning or implying any real relationship or orderof these elements or operations.

Although various embodiments of the present disclosure are describedabove, these embodiments neither present all details, nor imply that thepresent disclosure is limited to these embodiments. Obviously, manymodifications and changes may be made in light of the teaching of theabove embodiments. These embodiments are presented and some details aredescribed herein only for explaining the principle of the disclosure andits actual use, so that one skilled person can practice the presentdisclosure and introduce some modifications in light of the disclosure.The invention is intended to cover alternatives, modifications andequivalents that may be included within the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A super-junction structure comprising: an epitaxylayer of a first doping type; a plurality of first pillar regions of asecond doping type, which are formed in said epitaxy layer and separatedfrom each other, and a second pillar region, which is a portion of saidepitaxy layer between adjacent ones of said plurality of first pillarregions and arranged alternatively with said plurality of first pillarregions to form said super-junction structure, wherein each of saidplurality of first pillar regions comprises a first sub-pillar regionand a second sub-pillar region, said second sub-pillar region is stackedon said first sub-pillar region and has a doping concentration smallerthan that of said first sub-pillar.
 2. The super-junction structureaccording to claim 1, wherein said first sub-pillar region has a dopingconcentration larger that an average doping concentration of saidplurality of first pillar regions, and said second sub-pillar region hasa doping concentration less than an average doping concentration of saidplurality of first pillar regions, said average doping concentration isa doping concentration of said plurality of first pillar regions in acase that said plurality of first pillar regions have a uniform dopingconcentration and have a dopant amount equal to that of said secondpillar region.
 3. The super-junction structure according to claim 1,wherein said first doping type is an N type and said second doping typeis a P type.
 4. A semiconductor device, comprising: a semiconductorsubstrate; a super-junction structure according to claim 1, beingarranged above said semiconductor substrate; well regions of said seconddoping type, contacting top surfaces of said plurality of first pillarregions and a portion of said top surface of second pillar region;source regions of said first doping type, being arranged at surfaces ofsaid well regions; a gate oxide, being arranged above said second pillarregion, portions of said well regions and portions of said sourceregions; a polysilicon gate, being arranged above said gate oxide; afront-side metal layer contacting said source regions; and a back-sidemetal layer being arranged below and contacts said semiconductorsubstrate.
 5. The semiconductor device according to claim 4, furthercomprising an extension portion above said second pillar region, belowsaid gate oxide, and between adjacent ones of said well regions.
 6. Thesemiconductor device according to claim 5, further comprising contactregions at said surfaces of said well regions, wherein said front-sidemetal layer contacts said source regions and said contact regions.
 7. Asemiconductor device, comprising: a first semiconductor layer; asuper-junction structure according to claim 1, being arranged above saidsemiconductor substrate; and a second semiconductor layer above saidsuper-junction structure, wherein in a case that said firstsemiconductor layer is of said first doping type, said secondsemiconductor layer is of said second doping type, and in a case thatsaid first semiconductor layer is of said second doping type, saidsecond semiconductor layer is of said first doping type.
 8. A method formanufacturing a super-junction structure, comprising: forming anepitaxial layer of a first doping type; forming a plurality of firstsub-pillar regions of a second doping type in said epitaxial layer,wherein said plurality of first sub-pillar regions are separated fromeach other and have a first doping concentration; and forming aplurality of second sub-pillar regions of said second doping type onsaid plurality of first sub-pillar regions in said epitaxial layer,wherein said plurality of second sub-pillar regions have a second dopingconcentration smaller than said first doping concentration, wherein eachof said plurality of first sub-pillar regions is aligned in a verticaldirection to and connected to respective one of said plurality of secondsub-pillar regions to form respective one of a plurality of first pillarregions, and a portion of said epitaxy layer between adjacent ones ofsaid plurality of first pillar regions forms a second pillar region. 9.The method according to claim 8, wherein said first doping concentrationis larger than an average doping concentration of said first pillarregions, and said second doping concentration is less than said averagedoping concentration, and wherein said average doping concentration is adoping concentration of said plurality of first pillar regions in a casethat said plurality of first pillar regions have a uniform dopingconcentration and said plurality of first pillar region has a dopantamount equal to that of said second pillar region.
 10. The methodaccording to claim 9, wherein forming said epitaxial layer comprisesforming a plurality of first sub-epitaxial layers of said first dopingtype and a plurality of second sub-epitaxial layers of said first dopingtype, and said plurality of second sub-epitaxial layers are stacked onsaid plurality of first sub-epitaxial layers.
 11. The method accordingto claim 10, wherein forming said plurality of first sub-pillar regionscomprises doping said plurality of first sub-epitaxial layer with adopant of a second type to form a plurality of pillar regions which areseparated from each other and have said first doping concentration. 12.The method according to claim 10, wherein forming said plurality ofsecond sub-pillar regions comprises doping said plurality of secondsub-epitaxial layer with a dopant of a second type to form a pluralityof pillar regions which are separated from each other and have saidsecond doping concentration.
 13. The method according to claim 8, afterforming said epitaxial layer and before forming said first sub-pillarregions, further comprising forming a plurality of trenches in saidepitaxial layer, so that said second pillar region is located betweenadjacent ones of said plurality of trenches.
 14. The method according toclaim 13, wherein forming said plurality of first sub-pillar regionscomprises: filling lower portions of said plurality of trenches with afirst doped layer of said second doping type and having said firstdoping concentration; and forming said plurality of second sub-pillarregions comprises: filling upper portions of said plurality of trencheswith a second doped layer of said second doping type and having saidsecond doping concentration.
 15. The method according to claim 13,wherein forming said plurality of first sub-pillar regions comprises:doping bottoms of said plurality of trenches with a dopant of a secondtype; and forming said plurality of second sub-pillar regions comprises:filling said plurality of trenches with a doped layer of said seconddoping type and having said second doping concentration.